The present invention relates to a gear head of a manually guided power implement.
Such gear heads, especially of a brush cutter or the like, are provided with a tool shaft which is driven by a motor and by means of which a rotatable cutting tool, such as a saw blade, a mowing tool, a filament drum, or the like is driven. Part of the drive shaft is embodied as a cylindrically splined shaft having essentially coaxial grooves. Provided in this region are a pressure plate and an abutment plate having an abutment surface that is disposed essentially perpendicular to the longitudinal axis of the tool shaft, whereby the cutting tool is held between the abutment plate and the pressure plate at right angles to the axis of rotation. The abutment plate, the pressure plate, or even both components have a central opening that surrounds the tool shaft and on the inner side of which ribs are provided that are in engagement with the grooves. This provides a positive connection between the tool shaft and the abutment plate and/or the pressure plate in the direction of rotation. The cutting tool itself is clamped in a flush manner between the abutment plate and the pressure plate, whereby the transfer of torque is effected by frictional engagement.
Due to the high operating speed, it is necessary to provide a precise centering of the cutting tool in order to avoid an out of balance situation. For this purpose, the cutting tool has a circular central opening, the diameter of which is greater than that of the splined shaft. The abutment plate is provided with a central, cylindrical centering shoulder that engages in the circular opening of the cutting tool and ensures the ability of the tool to run true. Unfortunately, in practice mounting of the cutting tool is cumbersome and time consuming. The centering collar has a very low height that corresponds approximately to the thickness of the cutting tool. As a result, a cutting tool that has been correctly placed upon the abutment plate and the centering collar thereof can slide out of this position when the pressure plate is tightened, which makes the placement or exchange of the cutting tool unnecessarily difficult. If the cutting tool is clamped in a non-centered position, the resulting eccentricity effects an occasionally considerable vibration, which can mechanically greatly stress in particular the gear head. A recentering of the cutting tool is complicated, since the implement must be shut down and the clamping mechanism must again be released.
The aforementioned drawbacks are aggravated by a protective disk that is arranged between the cutting tool and the abutment surface of the abutment plate. The protective disk is held on the abutment plate together with the cutting tool, and is centered by the centering collar. A sliding of the cutting tool also permits a sliding or tilting of the protective disk, which increases the out of balance situation.
It is therefore an object for the present invention to improve a gear head of the aforementioned general type in such a way that a reliable centered mounting of a cutting tool is simplified.